Ionization Constants of Aqueous Amino Acids by Harvey Dent 2 Lyrics
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Ionization constants of aqueous amino acids at temperatures up to 250°C using hydrothermal pH indicators and UV-visible spectroscopy: Glycine, -alanine, and proline
Rodney G. F. Clarke, Christopher M. Collins, Jenene C. Roberts, Liliana N. Trevani, Richard J. Bartholomew, and Peter R. Tremaine
Department of Chemistry, Memorial University of Newfoundland, St. John's, NL, Canada A1B 3X7 2
Guelph-Waterloo Centre for Graduate Work in Chemistry, University of Guelph, Guеlph, ON, Canada N1G 2W13
University of Ontario Institute of Technology, Oshawa, ON, Canada L1H 7L7
(Rеceived January 20, 2004; accepted in revised form November 2, 2004)
Abstract
Ionization constants for several simple amino acids have been measured for the first time under hydrothermal conditions, using visible spectroscopy with a high-temperature, high-pressure flow cell and thermally stable colorimetric pH indicators
Uh, this method minimizes amino acid decomposition at high temperatures because the data can be collected rapidly with short equilibration times
The first ionization constant for proline and -alanine, Ka,COOH, and the first and second ionization constants for glycine, Ka,COOH and Ka,NH4, have been determined at temperatures as high as 250°C. Values for the standard partial molar heat capacity of ionization, rCpO, COOH and rCpO, NH4, have been determined from the temperature dependence of ln (Ka,COOH) and ln (Ka,NH4)
Now the methodology has been validated by measuring the ionization constant of acetic acid up to 250°C, which with results that agree with literature values obtained by potentiometric measurements to within the combined experimental uncertainty
We dedicate this paper to the memory of Dr. Donald Irish (1932–2002) of the University of Waterloo
Friend and former supervisor of two of the authors (R.J.B. and P.R.T.)
Chapter 1
Introduction
The properties of amino acids in hydrothermal solutions are of interest to biochemists and geochemists studying metabolic processes of thermophilic organisms and possible mechanisms for the origin of life at deep ocean vents. Thermophilic bacteria and archea have been found to exist at temperatures up to 121°C
Much more extreme conditions are encountered at deep ocean hydrothermal vents, where reduced aqueous solutions from deep under the sea floor are ejected into cold, oxidizing ocean water at temperatures and pressures that may reach near-critical and even super-critical conditions
The resulting solutions are rich in organic molecules, including amino acids and it has been postulated that similar hydrothermal vents on Primitive Earth may have been sites for the origin of life
(Baross and Demming, 1983; Trent et al., 1984; Yanagawa and Kojima, 1985; Miller and Bada, 1988; Shock, 1990, 1992; Bada et al., 1995; Crabtree, 1997)
This hypothesis is not without controversy, and it is an active topic of study through both field and laboratory investigations to investigate (gentlemen) mechanisms for the abiogenic synthesis of polypeptide molecules, reliable experimental thermodynamic data must be obtained, under hydrothermal conditions, for the speciation of amino acids, the formation of peptide bonds, and the complexation of amino acids with metal ions, both in the aqueous phase and at mineral interfaces the challenges in measuring thermodynamic constants for the amino acids under these conditions are formidable, and only a few quantitative studies at elevated temperatures have been reported
Heat-of-mixing flow calorimetry has been used to determine ionization constants and enthalpies of reaction for the protonation of the amino and carboxylate groups of several amino acids at temperatures of up to 125°C (Izatt et al., 1992; Gillespie et al., 1995; Wang et al., 1996)
Vibrating-tube densimeters and a Picker-type flow microcalorimeter have recently been used to determine experimental values for the standard partial molar volumes and heat capacities of glycine, -alanine-alanine (Alan), proline, and the dipeptide glycyl-gylcine, at temperatures as high as 275°C (Hakin et al.,1995, 1998; Clarke and Tremaine, 1999; Clarke et al., 2000)
We are aware of no other experimental studies on the thermodynamic properties of aqueous amino acids or peptides above 100°C amino acids exist in aqueous solutions at room temperature as zwitterions, HA(aq)
The carboxylate and ammonium ionic groups can ionize to yield protonated and deprotonated forms of the amino acid, according to the following equilibria: HA(aq) H2O(l) ` H2A(aq) OH(aq) (1) HA(aq) ` A(aq) H(aq) (2)
The equilibrium concentration of the nonzwitterionic form HAo (aq) is negligible at room temperature (Cohn and Edsall 1943)
The most widely reported methods for determining acid-base dissociation constants under hydrothermal conditions are potentiometric titrimetry and conductivity (Mesmer et al., 1970, 1997; Ho et al., 2000)
Conductivity measurements of amino acid ionization constants are impractical because, according to reactions 1 and 2, an excess of acid or base is required to drive the ionization. The use of pH titrations in the usual stirred hydrogen concentration cells (Mesmer et al., 1970) to study amino acids is limited to relatively low temperatures because amino acids have limited stability under hydrothermal conditions (Povoledo and Vallentyne, 1964; Vallentyne, 1964, 1968; Bada and Miller, 1970)
The length of time required to achieve Thermal equilibrium and to conduct the titration causes the amino acids to decompose
Although flow cells exist for potentiometric titrimetry (Sweeton et al., 1973; Lvov et al., 1999) they are complex to operate and have been used in only a few atudies (e.g., Patterson et al., 1982)
Recent work at the University of Texas (Austin) has identified five thermally stable colorimetric pH indicators, which have been used with success in UV-visible spectrophotometric flow cells to determine ionization constants of simple acids
Can I stop?
Now I'd like to read some acknowledgments:
There are many people that deserve credit for helping me to accomplish this
Educational landmark:
My parents, George and Christine, who have given me confidence and faith in myself
Through their constant love, support, and encouragement. My brother, Adam, who is just
Beginning his journey and helps me to see each day as a new adventure. My sister, Nancy
Who helps me to realize that many new challenges are waiting for me to explore. My
Grandmother, Blanche Francis, who taught me through her wisdom and vitality that every
Second of this life should be celebrated. My grandmother and aunt, Blanche and Joan Clarke
For their kindness and many carpentry projects that provided some weekend relief from my
Research
My supervisor, Dr. Peter Tremaine, and the hydrothermal chemistry group (past and
Present) for their help and support in the realm of chemistry. The staff of the machine shop
(especially Randy Thorn) and the electronics shop (especially Carl Mulcahy) at Memorial
University of Newfoundland for helping to keep my equipment running and my project on
Schedule. The amino acid analysis facility, also at Memorial University of Newfoundland
For their analysis of my solutions. Dr.Vladimir Majer for the use of his high temperature and
Pressure differential flow calorimeter at Universite Blaise Pascal in Clermont-Ferrand
France. This work was supported financially by the Natural Sciences and Engineering
Council of Canada, the International Association for the Properties of Water and Steam, and
Memorial University of Newfoundland
Finally, my fiance and best friend, Karen Leonard, for her patience and support over
The past four years. You have helped me through many difficult times and shared in all of my
Accomplishments both large and small. Without you, my life and this degree would not have
Been as good. And this is just the beginning of a wonderful life together
I want to read the whole page
Ionization constants of aqueous amino acids at temperatures up to 250°C using hydrothermal pH indicators and UV-visible spectroscopy: Glycine, -alanine, and proline
Rodney G. F. Clarke, Christopher M. Collins, Jenene C. Roberts, Liliana N. Trevani, Richard J. Bartholomew, and Peter R. Tremaine
Department of Chemistry, Memorial University of Newfoundland, St. John's, NL, Canada A1B 3X7 2
Guelph-Waterloo Centre for Graduate Work in Chemistry, University of Guelph, Guеlph, ON, Canada N1G 2W13
University of Ontario Institute of Technology, Oshawa, ON, Canada L1H 7L7
(Rеceived January 20, 2004; accepted in revised form November 2, 2004)
Abstract
Ionization constants for several simple amino acids have been measured for the first time under hydrothermal conditions, using visible spectroscopy with a high-temperature, high-pressure flow cell and thermally stable colorimetric pH indicators
Uh, this method minimizes amino acid decomposition at high temperatures because the data can be collected rapidly with short equilibration times
The first ionization constant for proline and -alanine, Ka,COOH, and the first and second ionization constants for glycine, Ka,COOH and Ka,NH4, have been determined at temperatures as high as 250°C. Values for the standard partial molar heat capacity of ionization, rCpO, COOH and rCpO, NH4, have been determined from the temperature dependence of ln (Ka,COOH) and ln (Ka,NH4)
Now the methodology has been validated by measuring the ionization constant of acetic acid up to 250°C, which with results that agree with literature values obtained by potentiometric measurements to within the combined experimental uncertainty
We dedicate this paper to the memory of Dr. Donald Irish (1932–2002) of the University of Waterloo
Friend and former supervisor of two of the authors (R.J.B. and P.R.T.)
Chapter 1
Introduction
The properties of amino acids in hydrothermal solutions are of interest to biochemists and geochemists studying metabolic processes of thermophilic organisms and possible mechanisms for the origin of life at deep ocean vents. Thermophilic bacteria and archea have been found to exist at temperatures up to 121°C
Much more extreme conditions are encountered at deep ocean hydrothermal vents, where reduced aqueous solutions from deep under the sea floor are ejected into cold, oxidizing ocean water at temperatures and pressures that may reach near-critical and even super-critical conditions
The resulting solutions are rich in organic molecules, including amino acids and it has been postulated that similar hydrothermal vents on Primitive Earth may have been sites for the origin of life
(Baross and Demming, 1983; Trent et al., 1984; Yanagawa and Kojima, 1985; Miller and Bada, 1988; Shock, 1990, 1992; Bada et al., 1995; Crabtree, 1997)
This hypothesis is not without controversy, and it is an active topic of study through both field and laboratory investigations to investigate (gentlemen) mechanisms for the abiogenic synthesis of polypeptide molecules, reliable experimental thermodynamic data must be obtained, under hydrothermal conditions, for the speciation of amino acids, the formation of peptide bonds, and the complexation of amino acids with metal ions, both in the aqueous phase and at mineral interfaces the challenges in measuring thermodynamic constants for the amino acids under these conditions are formidable, and only a few quantitative studies at elevated temperatures have been reported
Heat-of-mixing flow calorimetry has been used to determine ionization constants and enthalpies of reaction for the protonation of the amino and carboxylate groups of several amino acids at temperatures of up to 125°C (Izatt et al., 1992; Gillespie et al., 1995; Wang et al., 1996)
Vibrating-tube densimeters and a Picker-type flow microcalorimeter have recently been used to determine experimental values for the standard partial molar volumes and heat capacities of glycine, -alanine-alanine (Alan), proline, and the dipeptide glycyl-gylcine, at temperatures as high as 275°C (Hakin et al.,1995, 1998; Clarke and Tremaine, 1999; Clarke et al., 2000)
We are aware of no other experimental studies on the thermodynamic properties of aqueous amino acids or peptides above 100°C amino acids exist in aqueous solutions at room temperature as zwitterions, HA(aq)
The carboxylate and ammonium ionic groups can ionize to yield protonated and deprotonated forms of the amino acid, according to the following equilibria: HA(aq) H2O(l) ` H2A(aq) OH(aq) (1) HA(aq) ` A(aq) H(aq) (2)
The equilibrium concentration of the nonzwitterionic form HAo (aq) is negligible at room temperature (Cohn and Edsall 1943)
The most widely reported methods for determining acid-base dissociation constants under hydrothermal conditions are potentiometric titrimetry and conductivity (Mesmer et al., 1970, 1997; Ho et al., 2000)
Conductivity measurements of amino acid ionization constants are impractical because, according to reactions 1 and 2, an excess of acid or base is required to drive the ionization. The use of pH titrations in the usual stirred hydrogen concentration cells (Mesmer et al., 1970) to study amino acids is limited to relatively low temperatures because amino acids have limited stability under hydrothermal conditions (Povoledo and Vallentyne, 1964; Vallentyne, 1964, 1968; Bada and Miller, 1970)
The length of time required to achieve Thermal equilibrium and to conduct the titration causes the amino acids to decompose
Although flow cells exist for potentiometric titrimetry (Sweeton et al., 1973; Lvov et al., 1999) they are complex to operate and have been used in only a few atudies (e.g., Patterson et al., 1982)
Recent work at the University of Texas (Austin) has identified five thermally stable colorimetric pH indicators, which have been used with success in UV-visible spectrophotometric flow cells to determine ionization constants of simple acids
Can I stop?
Now I'd like to read some acknowledgments:
There are many people that deserve credit for helping me to accomplish this
Educational landmark:
My parents, George and Christine, who have given me confidence and faith in myself
Through their constant love, support, and encouragement. My brother, Adam, who is just
Beginning his journey and helps me to see each day as a new adventure. My sister, Nancy
Who helps me to realize that many new challenges are waiting for me to explore. My
Grandmother, Blanche Francis, who taught me through her wisdom and vitality that every
Second of this life should be celebrated. My grandmother and aunt, Blanche and Joan Clarke
For their kindness and many carpentry projects that provided some weekend relief from my
Research
My supervisor, Dr. Peter Tremaine, and the hydrothermal chemistry group (past and
Present) for their help and support in the realm of chemistry. The staff of the machine shop
(especially Randy Thorn) and the electronics shop (especially Carl Mulcahy) at Memorial
University of Newfoundland for helping to keep my equipment running and my project on
Schedule. The amino acid analysis facility, also at Memorial University of Newfoundland
For their analysis of my solutions. Dr.Vladimir Majer for the use of his high temperature and
Pressure differential flow calorimeter at Universite Blaise Pascal in Clermont-Ferrand
France. This work was supported financially by the Natural Sciences and Engineering
Council of Canada, the International Association for the Properties of Water and Steam, and
Memorial University of Newfoundland
Finally, my fiance and best friend, Karen Leonard, for her patience and support over
The past four years. You have helped me through many difficult times and shared in all of my
Accomplishments both large and small. Without you, my life and this degree would not have
Been as good. And this is just the beginning of a wonderful life together